Oil pressure warning light

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Hi guys....
i own a 89 vw fox ...ive had upper engine rebuild summer 2003...recent tuneup...new timing belt...new starter....new alternator...new rad...new coolant...new thermastat...newer temp sensor
heres my problem:
engine is at operating temp.(at operating temp guage reads anywhere from half way or just over half way mark but never into the warning end of the scale meaning my warning lite on the temp guage doesnt come on which would seem normal..
been driving say for more then a half an hour or longer..
temp outside right now these days is around -0 to -3 celuis range...
i'm running 0w30 synthetic oil and hastings oil filter..
at operating temp my car idles around 1000 rpms there abouts but quite steady...
at operating temp and when i'm idling the fox say at a train crossing or
even at a light if long enough for example when i picked up my wife at work and was idling the car in the parking lot for about 5 minutes my oil pressure light comes on..it flickers faintly to semi bright and by pressing the gas pedal and increasing idle rpms higher then 1000 rpms the light will go off...then taking my foot of the gas at idle the light will come back on but only flickers like i said earlier.

i've checked my oil level its filled to the max mark so its right up not low at all ...no oil loss between changes...
no visible oil leaks anywhere..
i said its cold here or colder then most other US cities right now ...but i'm not running a front cover over my vw grill so its not overheating or anything like that...
i'm starting to think the oil if been running since i changed it over a month and half ago(0w30 synthetic)was fine when the temp was colder about a month ago but since its warmed up around here...it maybe to thin of a oil causing a low oil pressure? is that possible?
does the fox run better on 10w30 or 10w40?
could it be a sensor thats attached to the oil filter causing it to misread?

thxs for any help in advance.

posted by  spinrite

Remove the oil pressure sending unit and install a pressure gage and see if the oil pressure is within specs @ idle @ at 1500 or 2000 rpm, warm engine. If normal, replace the sending unit or troubleshoot the wiring, if lower than spec, looking at a messed up oil filter, an oil pump , or serious engine work

posted by  tbaxleyjr

Okay, there are a few possibilities so let's give it a go.

1. First off I think the 0w-30 is probably too light a weight of oil, but I won't say for sure that is the cause. Reason being when I lived in that type of climate there was no such thing. In my opinion 10w-30 would be more appropriate.

2. Your engine has two oil pressure sending units. One on the oil filter adapter and one on the cylinder head. First and foremost make sure you have them installed in the right location. The head takes the brown on and the adapter takes the white one. If they're swapped or you have two the same color that may be your problem. I have no reason to believe this is a wiring problem due to the fact that it only happens at idle.

3. Now for the noise question. When the light starts to flicker do you hear any engine noise, specifically lifter noise from the top of the engine? If not your oil pressure is PROBABLY okay. If you have a direct reading oil pressure guage, by all means hook it up and test the pressure. For most people it's easier and cheaper to simply replace the sending units. Start with the brown one (cylinder head) as that is usually the first one to go. For peace of mind, anytime I have this problem on a customer car and it is the sender(s), I simply replace both of them. It's my experience that if one is bad the other is not far behind. It only costs them a few more dollars but saves everybody aggravation down the road.

posted by  vwhobo


The viscosity discussion is a good point. Although the owners manual in my three calls for 5W30 (preferred, 10W30 for warm weather), most of us in my part of the country use 10W30 - I havent had gage problems but it quitens down valve chatter on start-up esp on my Crown Vic. I had a similar problem on a 1990 Skylark 2.5L Ll-4 one summer drving through Southern Georgia en route to the beachs where the 10W30 viscosity brokedown and the oil pressure light would flicker somewhat when coming off of the exit ramp. No oil light when cold. No oil light when not driving the car as hard either. I quit using mobil dino oils at that point and used castrol until the group III mineral and group IV PAO synthetics became popular.

I haven't had much experience with the VWs but it is rather common on the Fords and some other domestics to have the sending units mess up on a regular basis.

posted by  tbaxleyjr

Plus, in my experience unless the engine isn't maintained properly, oil pump or bearing clearances are very seldom an issue. My wife's hide from radar, go to work at 80+mph, run the dogshit out of is an '85 Jetta with over 300k miles on it. The head and oil pan have never been off and it's oil pressure measures at the high side of good. These are stout engines, but the head mounted oil pressure sender tend to go bad from heat and vibration. I also put my money where my mouth is. When I do the annual t-belt replacement I replace both senders. Small money compared to getting the 'Honey, there's a light on my dash' call at 6 AM.

posted by  vwhobo

sounds like some of the type of calls I get ("what does the red light on my dash mean?)

posted by  tbaxleyjr

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